Add ellipsis constants.

pytest/Compiler/constants.py

@@ -61,3 +61,10 @@ def joined_string_constant():
   a = "I am" " still here"
   return a
 
+# CHECK-LABEL: func @ellipsis
+@import_global
+def ellipsis():
+  # CHECK: %[[A:.*]] = basicpy.singleton : !basicpy.EllipsisType
+  # CHECK: basicpy.unknown_cast %[[A]]
+  a = ...
+  return a

python/npcomp/compiler/frontend.py

@@ -210,6 +210,8 @@ class ExpressionImporter(BaseNodeVisitor):
         self.fctx.abort("unknown named constant '%r'" % (ast_node.value,))
     elif isinstance(ast_node, ast.Str):
       self.value = ir_h.basicpy_str_constant_op(ast_node.s).result
+    elif isinstance(ast_node, ast.Ellipsis):
+      self.value = ir_h.basicpy_singleton_op(ir_h.basicpy_EllipsisType).result
     else:
       self.fctx.abort("unknown constant type %s" %
                       (ast_node.__class__.__name__))